The present invention relates to a two-dimensional image detecting device which can detect an image of radiation such as an X-ray, a visible ray, or an infrared ray, and further concerns a manufacturing method thereof.
Conventionally, a two-dimensional image detecting device for radiation has been known in which semiconductor sensors for detecting an X-ray and for generating electrical charge (electron-hole pair) are two-dimensionally disposed, each sensor is provided with an electrical switch, and the electrical switches are successively turned on for each raw so as to read electrical charge for each column of the sensor.
A specific structure and principle of such a two-dimensional image detecting device are described in xe2x80x9cD. L. Lee, et al., xe2x80x98A New Digital Detector for Projection Radiographyxe2x80x99, Proc. SPIE, Vol. 2432, Physics of Medical Imaging, pp. 237-249, 1995 (published on Feb. 26, 1995)xe2x80x9d, xe2x80x9cL. S. Jeromin, et al., xe2x80x98Application of a-Si Active-Matrix Technology in a X-Ray Detector Panelxe2x80x99, SID(Society for Information Display) International Symposium, Digest of Technical Papers, pp. 91-94, 1997 (published on May 13, 1997)xe2x80x9d, and Japanese Laid-Open Patent Publication No.342098/1994 (Tokukaihei 6-342098, published on Dec. 13, 1994).
Referring to FIGS. 15 and 16, the following explanation describes the specific structure and principle of the conventional two-dimensional image detecting device for radiation. FIG. 15 is a perspective view schematically showing the construction of the two-dimensional image detecting device for radiation. Further, FIG. 16 is a sectional drawing schematically showing a structure for one pixel.
As shown in FIGS. 15 and 16, the two-dimensional image detecting device for radiation is provided with an active-matrix substrate 50 having electrode wires(gate electrode 52 and source electrode 53), a TFT(thin film transistor)54 and a storage capacitor(Cs)55, in an XY matrix form on a glass substrate 51. Moreover, a photoconductive film 56, a dielectric layer 57, and an upper electrode 58 are formed on virtually the entire surface of the active-matrix substrate 50.
The storage capacitor 55 has a construction in which a Cs electrode 59 opposes a pixel electrode 60 connected with a drain electrode of the TFT 54 via an insulating film 61.
As for the photoconductive film 56, semiconductive materials are used so as to generate electrical charge by exposure to radiation such as an X-ray. According to the aforementioned literatures, amorphous selenium(a-Se), which has high dark resistance and favorable photoconductivity, has been used for the photoconductive film 56. The photoconductive film 56 is formed with a thickness of 300-600 xcexcm by using a vacuum evaporation method.
Further, an active-matrix substrate, which is formed in a manufacturing process of a liquid crystal display device, can be applied to the active-matrix substrate 50. For example, an active-matrix substrate used for an active matrix liquid crystal display device(AMLCD) is provided with the TFT made of amorphous silicon(a-Si) or poly-silicon(P-Si), an XY matrix electrode, and a storage capacitor. Therefore, only a few changes in the arrangement make it easy to use the active-matrix substrate 50 for the two-dimensional image detecting device for radiation.
Referring to FIGS. 15 and 16, the following explanation describes a principle of operations of the two-dimensional image detecting device for radiation having the above-mentioned structure. Electrical charge is generated when the photoconductive film 56 is exposed to radiation. The photoconductive film 56 and the storage capacitor 55 are electrically connected in series with each other; thus, when voltage is applied between the upper electrode 58 and the Cs electrode 59, electrical charge generated in the photoconductive film 56 moves to a positive electrode side and a negative electrode side. As a result, the storage capacitor 55 stores electrical charge. Further, an electron blocking layer 62 made of a thin insulating layer is formed between the photoconductive film 56 and the storage capacitor 55. The electron blocking layer 62 acts as a blocking photodiode for preventing electrical charge from being injected from one side.
With the above-mentioned effect, the TFT 54 is turned on in response to input signals of gate electrode G1, G2, G3, . . . , and Gn so that the electrical charge stored in the storage capacitor 55 can be applied to the outside from source electrodes S1, S2, S3, . . . , and Sn. The gate electrodes 52 and source electrodes 53, the TFT 54, and the storage capacitor 55, etc. are all formed in a matrix form; therefore, it is possible to two-dimensionally obtain image information of an X-ray by scanning signals for each line inputted to gate electrodes G1, G2, G3, . . . , and Gn.
Additionally, when the photoconductive film 56 has photoconductivity for a visible ray and an infrared ray as well as for the radiation such as an X-ray, the above-mentioned two-dimensional image detecting device for radiation also acts as a two-dimensional image detecting device for detecting the visible ray and the infrared ray.
Incidentally, the conventional two-dimensional detecting device for radiation has used a-Se for the photoconductive film 56. Since the a-Se does not have sufficient responsivity to an X-ray, the storage capacitor 55 needs to be exposed to the X-ray for a long time to be fully charged, before reading information, and it takes a long time to return the photoconductive layer 56 to the initial state after X-ray irradiation is shielded.
Further, in order to reduce leakage current(dark current) and to provide a protection against high voltage, the dielectric layer 57 is provided between the upper electrode 58 and the photoconductive film 56 made of a-Se. However, it is necessary to add a step(sequence) for removing electrical charge remained in the dielectric layer 57 for each frame; thus, the above-mentioned two-dimensional image detecting device can be used only for photographing a static picture.
In response to this problem, in order to obtain image data corresponding to a moving image, it is necessary to use the photoconductive film 56 which is superior in responsivity and sensitivity to X-ray. As the photoconductive materials, CdTe and CdZnTe, whose effective atomic number is larger than that of Se, have been known. However, when CdTe or CdZnTe is adopted instead of a-Se as a material of the photoconductive film 56 of the two-dimensional image detecting device for radiation, the following problem arises:
In the case of the conventional a-Se, a vacuum evaporation method can be adopted as a film-forming method and a film can be formed at a normal temperature; thus, it has been easy to form a film on the active-matrix substrate 50. Meanwhile, in the case of CdTe and CdZnTe, film-forming methods such as an MBE(molecular beam epitaxy)method and an MOCVD(metal organic chemical vapor deposition)method have been known. Especially in view of forming a film on a large substrate, it is understood that the MOCVD method is appropriate. However, when a material such as CdTe and CdznTe is made into a film by using the MOCVD method, a high temperature of approximately 400xc2x0 C. is required for forming a film.
Generally, in the TFT 54 which is formed on the active-matrix substrate 50, an a-Si film or a p-Si film is used as a semiconductive layer. The a-Si film and the p-Si film are formed at a film-forming temperature of 300-350xc2x0 C. while hydrogen(H2) being added, in order to improve the semiconductive property. The TFT element formed in such a process has a heat-resistance temperature of approximately 300xc2x0 C. If the TFT element is exposed at a temperature exceeding the heat-resistance temperature, hydrogen is released from the a-Si film and the p-Si film; consequently, the conductive property is degraded.
Therefore, in view of the film-forming temperature, it has been practically difficult to make a material such as CdTe and CdZnTe into a film on the active-matrix substrate 50 by using the MOCVD method.
The present invention is devised to solve the above-mentioned problem. The objective is to provide a two-dimensional image detecting device which has favorable responsivity and detect a moving image, and a manufacturing method thereof.
In order to achieve the above objective, the two-dimensional image detecting device of the present invention (hereinafter, referred to as the present image detecting device), in which a pixel substrate and an opposing substrate oppose each other, the pixel substrate having a pixel alignment layer including a plurality of pixels, the opposing substrate having a photoconductive layer for generating electrical charge in accordance with incident light, is provided with conductive connecting members which are disposed so as to correspond to the pixels of the pixel alignment layer and which electrically connect the pixel alignment layer and the photoconductive layer, and space keeping members for keeping a space between the substrates.
In the present image detecting device, the pixel substrate and the opposing substrate are disposed so as to oppose each other. The pixel alignment layer is provided on the pixel substrate, and the photoconductive layer is provided on the opposing substrate.
The photoconductive layer disposed on the opposing substrate is a thin film which generates electrical charge in response to incident light (radiation, etc.) and is made of, for example, a semiconductive film. Further, the photoconductive layer is disposed so as to oppose the pixel alignment layer of the pixel substrate.
The pixel alignment layer has a plurality of pixels for accumulating electrical charge transmitted from the outside. For example, an active-matrix substrate is available, in which switching elements having pixel electrodes are arranged in a lattice form. Moreover, the pixels of the pixel alignment layer are connected with the photoconductive layer via the conductive connecting members.
In the present image detecting device, voltage is applied between the pixel alignment layer and the photoconductive layer, so that electrical charge appearing from the photoconductive layer in response to incident light is transmitted and accumulated into each of the pixels on the pixel alignment layer.
And then, pixels which accumulate electrical charge are identified so as to detect an image which enters the photoconductive layer.
Further, particularly, the present image detecting device has the pixel alignment layer and the photoconductive layer formed on the different substrates, so that the photoconductive layer is not formed on the pixel alignment layer. This arrangement can prevent a heating operation performed on the photoconductive layer from adversely affecting the pixel alignment layer.
Therefore, regarding the present image detecting device, it is possible to adopt a material which has high responsivity and sensitivity to incident light and requires a heating operation at a high temperature, as a material for the photoconductive layer. Hence, the responsivity can be improved upon detecting a two-dimensional image.
Furthermore, such a material (for example, a CdTe or CdZnTe compound semiconductor) can reduce voltage applied to the photoconductive layer, so that it is not necessary to provide a dielectric layer for protecting the photoconductive layer from high voltage. Hence, it is possible to eliminate the need for a process which removes electrical charge remaining on the dielectric layer. Consequently, continuous image detection, namely, moving image detection can be realized.
Further, the present image detecting device is provided with the space keeping members for keeping a space between the substrates. This arrangement can prevent a space (gap) between the substrates from becoming too small, upon bonding and connecting the substrates. Thus, it is possible to prevent damage on the conductive connecting members and a contact between the adjacent conductive connecting members (defect caused by leakage).
Moreover, in order to achieve the aforementioned objective, a manufacturing method of a two-dimensional image detecting device in accordance with the present invention (hereinafter, referred to as the present manufacturing method), the two-dimensional image detecting device including a pixel substrate which is provided with a pixel alignment layer having a plurality of pixels, and an opposing substrate which is provided with a photoconductive layer for generating electrical charge in response to incident light, the method including the steps of: a connecting member forming step for forming conductive connecting members on one of the substrates in accordance with the pixels of the pixel alignment layer; a keeping member forming step for forming space keeping members, which keep a space between the substrates, on one of the substrates; and a connecting step for bonding the substrates such that the pixel alignment layer and the photoconductive layer oppose each other.
The present manufacturing method is devised for manufacturing a two-dimensional image detecting device, in which the photoconductive layer and the pixel alignment layer are formed on the different substrates, like the present image detecting device. Namely, in the present manufacturing method, the photoconductive layer is not formed on the pixel alignment layer. Thus, it is possible to adopt a material which has high responsivity and sensitivity to incident light and requires a heating operation at a high temperature.
This method makes it possible to manufacture the two-dimensional image detecting device which can detect a moving image with high responsivity.
Furthermore, in the present manufacturing method, the pixel substrate and the opposing substrate are connected to each other via the conductive connecting members provided in accordance with the pixels of the pixel alignment layer. This arrangement makes it possible to electrically connect the pixels and the photoconductive layer while securing electrical insulation between the pixels. Consequently, it is possible to manufacture the two-dimensional image detecting device which causes no crosstalk.
Additionally, in the present manufacturing method, the space keeping members are formed on one of the substrates before the substrates are bonded to each other. This arrangement makes it possible to prevent a space between the substrates from becoming too small in the connecting step. Therefore, it is possible to prevent damage on the conductive connecting members and a contact between the adjacent conductive connecting members.
Further, the space keeping members and the conductive connecting members are preferably formed by patterning the photosensitive resin, etc. Thus, it is possible to readily form the space keeping members and the conductive connecting members into desired shapes. Moreover, when the conductive connecting members are formed by patterning, it is possible to readily obtain electrical insulation between the pixels of the pixel alignment layer. Consequently, crosstalk can be prevented between the adjacent pixels.
Furthermore, the space keeping members are formed by patterning, so that the space keeping members and the conductive connecting members can be formed separately with ease. Therefore, it is possible to prevent deformation and property degradation of the conductive connecting members upon bonding the substrates.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.